The present invention relates to a multiple fibre forming machine permitting a simultaneous drawing of a plurality of optical fibres and then a linear multifibre stranding. It is used in the construction of cables intended for optical telecommunications.
Two stages are involved in the production of a multifibre cable. Firstly, an optical fibre is drawn and stored temporarily on reels or drums and then the stranding operation is performed with the same number of storage reels or drums as there are to be fibres in the cables.
More specifically, in a conventional optical fibre drawing installation, a preform made from a suitable material (e.g. silica) is formed into fibres at a speed of approximately 30 m/minute. The fibre obtained is then coated with a covering product and stored on a drum.
Every effort is made to store the maximum fibre lengths so as to be to appropriately supply the stranding machine. However, the obtaining of very great fibre lengths would appear to be not easily compatible with the presently available drawing processes, so that in practice splicing operations are necessary to obtain great lengths.
Moreover, a stranding machine generally comprises an extruder, which supplies a cable support having recesses which are able to receive the fibres, an assembly and connecting means which appropriately places the fibres in the recesses and finally a means for covering the cable with a protective sheath. The cable is produced at a speed of approximately a few meters per minute.
The operating procedure according to the prior art has a number of disadvantages. It involves a number of stages and raises the problem of the compatibility of the fibre formation and stranding speeds. In order to make the best possible use of the assembly and connecting means of the stranding machine, it is necessary to have a plurality of drawing machines upstream of the stranding machine, so that costs are high and the installation is of a complex nature.
This difficulty is a handicap for optical fibres in competition with conventional electrical cables. The situation is in fact much more favourable for the latter because the basic wire can be produced at speeds of approximately 1,200 to 1,600 m/minute over very considerable length (50 to 100 km) and only a single drawing machine is required for supplying the stranding installation.